Touch Pixel Structure With Reference Capacitor and Dielectric Shielding
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Solution Overview
Problem
Current touch sensors face limitations in achieving high resolution and large area coverage due to parasitic capacitance and signal noise issues, making them less effective for secure authentication and biometric applications.
Innovation Solution
A touch sensitive pixel structure comprising a thin film transistor, capacitive sensing electrode, and reference capacitor, with layers deposited using metallisation techniques to address parasitic capacitance and signal noise, and a dielectric shield providing improved encapsulation and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive matrix capacitive touch sensing systems are used with external driving circuits, then device complexity is reduced, but measurement precision and reliability deteriorate due to environmental noise and interference
Solution Approach 1:
A shielding layer is introduced as an intermediary between the sensing electrode and the environment. This shielding layer acts as a mediator that blocks environmental noise and interference from reaching the sensing electrode, thereby improving measurement precision without requiring complex active matrix circuits.
2Measurement precision
If active matrix capacitive touch sensors are used with switching elements in each pixel, then measurement precision improves, but device complexity increases
Solution Approach 1:
The complex switching elements and active matrix circuitry are extracted and removed from each pixel. Instead, a simplified passive matrix structure with shielding layers is used, which achieves adequate sensing precision without the complexity of active matrix implementations.
3Measurement precision
If high resolution fingerprint sensing is implemented with hundreds of pixels per inch, then measurement precision improves, but manufacturing difficulty increases
Solution Approach 1:
Instead of increasing pixel density in the planar dimension to achieve higher resolution, the invention adds a vertical dimension by introducing multiple shielding layers at different depths. This three-dimensional layered structure enables high-resolution sensing through depth-based differentiation rather than solely through increased pixel count.
4Area of stationary object
If large area touch sensors are manufactured, then area coverage increases, but parasitic capacitance accumulates additively limiting performance
Solution Approach 1:
The large-area sensor is segmented into multiple independent sensing regions with individual shielding layers for each region. This segmentation prevents parasitic capacitance from accumulating additively across the entire large area, as each segmented region with its own shielding layer operates independently with localized parasitic capacitance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables high-resolution, large-area touch sensors with improved sensitivity and performance, enhancing secure authentication and biometric applications by reducing parasitic capacitance and signal noise.
Implementation Method 1
The capacitive sensing electrode 14 accumulates a charge in response to proximity of a surface of a conductive object to be sensed by the pixel
Implementation Method 2
The conduction path of the sense VCI 2020 connects the first plate 161 of the reference capacitor 16, and so also the control voltage, to an input of a readout circuit 2026
Implementation Method 3
A touch sensitive pixel structure comprising a thin film transistor, capacitive sensing electrode, and reference capacitor, with layers deposited using metallisation techniques to address parasitic capacitance and signal noise, and a dielectric shield providing improved encapsulation and sensitivity
Data Source
AI summary
Disclosed herein is a pixel structure comprising a plurality of layers for providing a touch sensitive pixel of a sensing array. The pixel comprises: a thin film transistor, a capacitive sensing electrode, and a reference capacitor comprising a first plate and a second plate. The capacitive sensing electrode and the second plate of the reference capacitor are connected to a gate region of the thin film transistor. Methods of manufacturing such a touch sensitive pixel are also disclosed herein.